As an existing controller of an air-conditioning system, there is a controller including a feedback controller (PID controller) for automatically controlling a predetermined process (see, e.g., Patent Literature 1). The PID controller including the PID controller changes output of the PID controller stepwise within a certain range. At this time, the PID controller identifies parameters (dead time, a primary delay time constant, and process gain) on the basis of output of a control target. Then, the PID controller determines parameters of the PID controller on the basis of a predetermined equation by using the parameters of the control target.